Colors only process to reduce package yield loss

ABSTRACT

Disclosed is an ordered microelectronic fabrication sequence in which color filters are formed by conformal deposition directly onto a photodetector array of a CCD, CID, or CMOS imaging device to create a concave-up pixel surface, and, overlayed with a high transmittance planarizing film of specified index of refraction and physical properties which optimize light collection to the photodiode without additional conventional microlenses. The optically flat top surface serves to encapsulate and protect the imager from chemical and thermal cleaning treatment damage, minimizes topographical underlayer variations which would aberrate or cause reflection losses of images formed on non-planar surfaces, and, obviates residual particle inclusions induced during dicing and packaging. A CCD imager is formed by photolithographically patterning a planar-array of photodiodes on a semiconductor substrate. The photodiode array is provided with metal photoshields, passivated, and, color filters are formed thereon. A transparent encapsulant is deposited to planarize the color filter layer and completes the solid-state color image-forming device without conventional convex microlenses.

This is a division of U.S. patent application Ser. No. 11/642,225, filedDec. 20, 2006, now U.S. Pat. No. 7,485,906, which is a continuation ofU.S. patent application Ser. No. 11/037,445, filed Jan. 18, 2005, nowU.S. Pat. No. 7,183,598, which is a continuation of U.S. patentapplication Ser. No. 10/272,136, filed Oct. 16, 2002, by now issued U.S.Pat. No. 6,876,049, which is a divisional application of U.S. patentapplication Ser. No. 09/867,379, filed May 30, 2001, now issued as U.S.Pat. No. 6,482,669, the entire contents of which applications andpatents are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to light collection efficiency and packageyield improvements for the optical structure and microelectronicfabrication process of semiconductor color imaging devices.

BACKGROUND

Synthetic reconstruction of color images in solid-state analog ordigital video cameras is conventionally performed through a combinationof an array of optical microlens and spectral filter structures andintegrated circuit amplifier automatic gain control operations followinga prescribed sequence of calibrations in an algorithm.

Typically solid-state color cameras are comprised of charge-coupleddevice (CCD), Charge-Injection Device (CID), or ComplementaryMetal-Oxide Semiconductor (CMOS) structures with planar arrays ofmicrolenses and primary color filters mutually aligned to an area arrayof photodiodes patterned onto a semiconductor substrate. The principalchallenge in the design of solid-state color camera devices is thetrade-off between adding complexity and steps to the microelectronicfabrication process wherein color filters are integrally formed in thesemiconductor cross-sectional structure versus adding complexity andintegrated electronic circuitry for conversion of the optical analogsignals into digital form and signal processing with color-specificautomated gain-control amplifiers requiring gain-ratio balance. Thetrade-off between microelectronic fabrication process complexity versuselectronic complexity is determined by a plurality of factors, includingproduct manufacturing cost and optoelectronic performance.

Color-photosensitive integrated circuits require carefully configuredcolor filters to be deposited on the upper layers of a semiconductordevice in order to accurately translate a visual image into its colorcomponents. Conventional configurations may generate a color pixel byemploying four adjacent pixels on an image sensor. Each of the fourpixels is covered by a different color filter selected from the group ofred, blue and two green pixels, thereby exposing each monochromaticpixel to only one of the three basic colors. Simple algorithms aresubsequently applied to merge the inputs from the three monochromaticpixels to form one full color pixel. The color filter deposition processand its relationship to the microlens array formation process determinethe production cycle-time, test-time, yield, and ultimate manufacturingcost. It is an object of the present invention to teach color-filterprocesses which optimize these stated factors without the microlensarray(s) and the associated complex process steps.

While color image formation may be accomplished by recordingappropriately filtered images using three separate arrays, such systemstend to be large and costly. Cameras in which a full color image isgenerated by a single detector array offer significant improvements insize and cost but have inferior spatial resolution. Single-chip colorarrays typically use color filters that are aligned with individualcolumns of photodetector elements to generate a color video signal. In atypical stripe configuration, green filters are used on every othercolumn with the intermediate columns alternatively selected for red orblue recording. To generate a color video signal using an array of thistype, intensity information from the green columns is interpolated toproduce green data at the red and blue locations. This information isthen used to calculate a red-minus-green signal from red-filteredcolumns and a blue-minus-green signal from the blue ones.

Complete red-minus-green and blue-minus-green images are subsequentlyinterpolated from this data yielding three complete images. Commercialcamcorders use a process similar to this to generate a color image buttypically utilize more complicated mosaic-filter designs. The use ofalternate columns to yield color information decreases the spatialresolution in the final image.

The elementary unit-cell of the imager is defined as a pixel,characterized as an addressable area element with intensity and chromaattributes related to the spectral signal contrast derived from thephoton collection efficiency. Prior art conventionally introduces amicrolens on top of each pixel to focus light rays onto thephotosensitive zone of the pixel.

The optical performance of semiconductor imaging arrays depends on pixelsize and the geometrical optical design of the camera lens, microlenses,color filter combinations, spacers, and photodiode active area size andshape. The function of the microlens is to efficiently collect incidentlight falling within the acceptance cone and refract this light in animage formation process onto a focal plane at a depth defined by theplanar array of photodiode elements. Significant depth of focus may berequired to achieve high resolution images and superior spectral signalcontrast since the typical configuration positions the microlens arrayat the top light collecting surface and the photosensors at thesemiconductor substrate surface.

When a microlens element forms an image of an object passed by a videocamera lens, the amount of radiant energy (light) collected is directlyproportional to the area of the clear aperture, or entrance pupil, ofthe microlens. At the image falling on the photodiode active area, theillumination (energy per unit area) is inversely proportional to theimage area over which the object light is spread. The aperture area isproportional to the square of the pupil diameter and the image area isproportional to the square of the image distance, or focal length. Theratio of the focal length to the clear aperture of the microlens isknown in Optics as the relative aperture or f-number. The illuminationin the image arriving at the plane of the photodetectors is inverselyproportional to the square of the ratio of the focal length to clearaperture. An alternative description uses the definition that thenumerical aperture (NA) of the lens is the reciprocal of twice thef-number. The concept of depth of focus is that there exists anacceptable range of blur (due to defocussing) that will not adverselyaffect the performance of the optical system. The depth of focus isdependent on the wavelength of light, and, falls off inversely with thesquare of the numerical aperture. Truncation of illuminance patternsfalling outside the microlens aperture results in diffractive spreadingand clipping or vignetting, producing undesirable nonuniformities and adark ring around the image.

The limiting numerical aperture or f-stop of the imaging camera'soptical system is determined by the smallest aperture element in theconvolution train. Typically, the microlens will be the limitingaperture in video camera systems. Prior Art is characterized by methodsand structures to maximize the microlens aperture by increasing theradius of curvature, employing lens materials with increased refractiveindex, or, using compound lens arrangements to extend the focal planedeeper to match the multilayer span required to image light onto theburied photodiodes at the base surface of the semiconductor substrate.Light falling between photodiode elements or on insensitive outer zonesof the photodiodes, known as dead zones, may cause image smear or noise.With Industry trends to increased miniaturization, smaller photodiodesare associated with decreasing manufacturing cost, and, similarly,mitigate against the extra steps of forming layers for Prior Artcompound lens arrangements to gain increased focal length imaging. Sincethe microlens is aligned and matched in physical size to shrinking pixelsizes, larger microlens sizes are not a practical direction. Higherrefractive index materials for the microlens would increase thereflection-loss at the air-microlens interface and result in decreasedlight collection efficiency and reduced spectral signal contrast orreduced signal-to-noise ratio. Limits to the numerical aperture value ofthe microlens are imposed by the inverse relationship of the depth offocus decreasing as the square of the numerical aperture, a strongquadratic sensitivity on the numerical aperture.

Typically, a pixel with a microlens requires a narrower incident lightangle than a pixel that does not use a microlens, imposing additionaloptical design implications for the lens of the camera.

The design challenge for creating superior solid-state color imagers is,therefore, to optimize spectral collection efficiency to maximize thefill-factor of the photosensor array elements without vignetting (lossesfrom overfilling) and associated photosensor cross-talk, and, with theminimum number of microelectronic fabrication process steps. The presentinvention is clearly distinguished from Prior Art by introducing atleast one high transmittance planar film-layer of specified optical andphysical properties directly over color-filters without the use ofmicrolens arrays.

This distinction will be further demonstrated in the following sectionsby describing the specific related optical conditions to be satisfied atthe interfaces between the functional layers comprising thesemiconductor color-imaging device when no microlenses are used.

On colors only products where no microlens layer is formed, the colorpixel surface is not flat. The curvature of the color filter surfacewill cause incident image light to refract and the image position andpower-density (viz., irradiance distribution) at the sensor surface willbe changed. These factors could have an effect on pixel sensitivity,signal contract and pixel cross-talk. In the colors only process, thefinal product wafer suffers significant topography step-heightvariations. During the package dicing step, residue particles remainembedded as a result of the topographical problem. The resultingentrapped residue particles impact the image quality and cause yieldloss of CMOS/CCD image sensor products.

FIG. 1 exhibits the conventional Prior Art vertical semiconductorcross-sectional profile and optical configuration for color imageformation. Microlens 1 residing on a planarization layer which serves asa spacer 2 collects a bundle of light rays from the image presented tothe video camera and converges the light into focal cone 3 ontophotodiode 8 after passing through color filter 4 residing onplanarization layer 5, passivation layer 6, and metallization layer 7.

The purpose of the microlens' application in CCD and CMOS imagingdevices is to increase imager sensing efficiency. FIG. 2 illustrates thegeometrical optics for incident image light 9 converged by microlenselement 10, color filter 11, into focal cone 12, to the focal area 13within a photoactive area 14 surrounded by a dead or non-photosensitivearea 15, wherein the sum of the areas of 14 and 15 comprise the regionof the pixel.

Qtsuka in U.S. Pat. No. 6,040,591 teaches a charge-coupled device (CCD)imaging array having a refractive index adjusting and planarizing layerover a microlens array layer to correct for non-normal angles ofincidence affect on the image light convergence positions at thephotosensor planar array and for interfacial reflection loss at themicrolens surface. Otsuka assumed a typical refractive index value ofn=1.75 for a reflowed polyimide resin microlens and selected afluororesm from Asahi Glass Co., Ltd of refractive index n=1.34 for theindex adjusting layer. That is, Otsuka uses an index of refraction forthe refractive index adjusting layer which is lower than the microlen'sindex to assure bending image light rays inward toward thesurface-normal to obviate vignetting at the sensor active area. FIG. 3shows the CCD cross-sectional structure of the preferred embodiment ofOtsuka's referenced patent, comprised of a photodiode 28, chargetransfer portion 17, formed in a semiconductor substrate 16, having avertical transfer electrode 18, a light shielding film 19 covering thevertical transfer electrode 18, a transparent flattening film 20,covering the photodiode 28 and light shielding film 19, a color filter21 formed on the flattening film 20, a flattening film 22 formed on thecolor filter 21, a hemispherical microlens 23 formed on the transparentflattening film 22, and a transparent film 24 having refractive indexlower than that of the microlens formed to cover the microlens. A finaloptional top-surface antireflection coating 25 is then formed on thefilm 24. Incident light, L, is shown to converge at the new, deeperfocal point F, instead of the unadjusted shallower value of f0 whichoccurs when the index-adjusting film 24 is absent. It is noted, then,that the indices of refraction and all the prescribed layer thicknessestaught by Otsuka in the referenced patent correspond to optical designsaccommodating the geometric and physical optical characteristics of theformed microlens, not those of the color filter layer(s). No specialtreatment or specified conditions are provided for adjustment of theplanarizing spacer layer 22, nor are interface conditions between thecolor filter layers 21 and planarizing spacer layer 22 addressed. Thecase of no microlens is not considered by Otsuka. Otsuka does considerusing the index-adjusting layer as a transparent sealing resin which canbe hardened and used to seal the solid-state imager as a package. It isnoted that any contaminants captured in the microlens interstices willnot be removed in a final cleaning process step, but will be sealed inas well. Results of embedded particulates will lead to light scatteringnoise effects.

An alternative approach to microlens optics and device cross-sectionaladaptations, using refractive index structures configured to collect andconverge image light onto the photodetecting surface of the pixel, isgiven by Furumiya in U.S. Pat. No. 5,844,290. It is noted that colorfilters, color image formation processes, and whether there iscompatibility of Furiyama's structures with color filters are notdiscussed in Furiyama's referenced patent.

According to FIG. 4 in U.S. Pat. No. 5,844,290 by Furiyama, a preferredembodiment for the solid-state imager is comprised of a CCD structureformed of n-type silicon substrate 30, p-well 31, silicon-oxide film 38,in which are patterned n-type buried channel layer 34 above p-type layer35, a pn junction photodiode of p+ type layer 33 above n-type layer 32with p+ device isolation 36, and, device opening 42 and reading gate 34.Built up above the pn junction are transfer electrode 39, silicon oxidefilm 40, light shield film 41, insulator film 43, and, a first region ofplanarizing resin 45 vertically contiguous with a second region ofplanarizing resin layer 44, forming a top surface plane for microlensarray 46.

The geometrical optics for capturing and converging image light to thephotosensor plane of the CCD is depicted by normal incident light Igathered in a focal cone of the microlens. The extreme rays arerefracted by the second (vertical) region of planarizing resin layer 44into the first region of planarizing resin layer 45, to a focal point inproximity to the photodiode surface. The first region 45 is in the formof a cylindrical column and is positioned between the n-type layer 32and a center portion of the microlens 46. The second region 44surrounding the first region 45 has a refractive index larger than arefractive index of the first region, assuring the image light bendsinwards toward the surface normal. This coaxial cylindrical arrangementcan, as Furumiya states, be subject to reflection losses at the boundarybetween the planarizing resin layers. It is noted here for the Furumiyareferenced patent, as well as we noted earlier for the Otsuko referencedpatent, that the case of no microlens is not addressed.

U.S. Pat. No. 5,691,548 to Akio addresses the long focal length, filmstack thickness, and vignetting problems common in Prior Art byintroducing a compound lens arrangement comprised of a first positive orconverging convex element in tandem with a negative or diverging(concave upward) second element. The principal problem Akio addresses isfor low light levels the camera's aperture stop must be fully opened.Obliquely incident light rays will noticeably increase in theirproportion to the total amount of all incident image light. Under theseconditions, conventional solid-state imagers will truncate or vignettesignificantly, diminishing their optical sensitivity.

To solve this problem of conventional imagers not collecting and imaginglight efficiently when the aperture is open fully, Akio teaches anoptical arrangement so that a concave type microlens layer operates tocollimate light rays collected by the convex lens so as to converge onthe photosensor plane. The color image formation process and the case ofno microlens is not addressed in the referenced Akio patent.

In U.S. Pat. No. 6,091,093 to Kang et al, an MOS semiconductor imagerand microlens process is taught. In particular, embodiments of theinvention are directed to create a number of gate islands electricallyinsulated from each other with spacers. The processes disclosed aims tointegrate logic IC fabrication with photosensors. Conventional processesfor polycide-gate or salicide-gate MOS devices generally introduce theproblem of inherently forming opaque regions preventing image light fromentering the photosensitive regions of the silicon at a distance belowthe surface. Kang et al teach a process for photocell constructionwithout the conventional additional mask step to prevent the formationof the silicide over those silicon regions that are patterned forphotodetectors. Spacers are formed above the pn-junction of thephotodiode array elements such that incident light passes through thespacers and into the photosensitive region. As noted previously, Kangdoes not address the color formation process and his opticalarrangements will not operate without a converging microlens.

The color filter process and optical film structures taught in thepresent invention are clearly distinguished from the Prior Art byeliminating microlenses, and, are shown to include fewer process stepswith improved package final product yield.

SUMMARY

A principal object of the present invention is to teach the method andstructures for adding a specified planarization layer after the finalcolor filter layer formation in the colors only product in which thereare no microlenses. Experiments conducted by the inventors havedemonstrated that the present invention improves pixel sensitivity andreduces the package yield loss through the reduction of residual trappedparticulates induced in the package dicing and cleaning steps. It is anobject of the present invention to reduce interfacial reflection lossesand vignetting of image light by disclosing a method, structures andoptical properties required for refractive index boundary-engineering.

Another object of the present invention is to provide an adaptiveprocess wherein antireflection and image-forming structures, spectralcolor filters, and, combinations or varying configurations ofsemiconductor vertical profiles can be integrated with the result ofmaximizing collection efficiency of image intensity patterns on thephotodiode planar arrays to achieve optimum pixel resolution and colorsignal contrast with minimal smear and pixel cross-talk.

In accord with a principal object of the present invention, there isprovided by the present invention a manufacturing method andmicroelectronic fabrication process sequence which minimizes the numberand task-times of the operational steps required in the production ofsemiconductor arrays for color imaging devices.

Another object of the present invention is to provide an overcoatprocess allowing the widest and most forgiving process windows for colorfilters and semiconductor integration reproducibility, high reliability,and, consequently maximum process and package yield.

A further object of the present invention is to obviate topographicalstep variations, non-planarity and surface roughness problemsencountered with conventional Prior Art formation sequences. Prior Artis well known to have step-height or steric effect variations betweenR/G/B layers and results in departures from designer's specifications intransmittance color-balance.

Avoidance of the specific color pixel lifting problem is a still furtherobject of the present invention.

To practice the method of the present invention, conventionalmicroelectronic fabrication techniques using photolithographicmaterials, masks and etch tools are employed: in succession the array ofpn-junction photodiodes is patterned with impurity dopants diffused orion-implanted, electrically isolated, and planarized over. In thepresent invention, the colors only process is disclosed wherein colorfilters are geometrically patterned to assemble primary green, red, andblue color filters formed by the addition of suitable dyes or pigmentsappropriate to the desired spectral transmissivity to be associated withspecified photodetector coordinate addresses in the imager matrix andthe algorithm for synthetic color image reconstruction. The microlensprocess steps have been eliminated in the colors only process. A finalspecified planarization layer is applied directly above the color filterlayer to complete the colors only process. The flat top surface isoptimal for the package dicing and final cleaning treatment steps,minimizing particle residues and maximizing product final yield.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention areunderstood within the context of the Description of the PreferredEmbodiment, as set forth below. The Description of the PreferredEmbodiment is understood within the context of the accompanyingdrawings, which form a material part of this disclosure, wherein:

FIG. 1 is a simplified schematic cross-sectional profile ofsemiconductor and optical structures showing a typical order of elementsof a conventional Prior Art device for color image formation.

FIG. 2 illustrates the geometrical optics factors for microlens imagingonto the photosensitive active zone within a square pixel area.

FIG. 3 depicts the cross-sectional structure and image convergingoptical paths for a Prior Art CCD imager with a single-layer microlens,refractive index adjusting overcoat and top surface antireflection filmlayer.

FIG. 4 demonstrates a Prior Art cross-sectional structure and imagelight collection scheme using vertical coaxial cylindrical sections ofhigher and lower refractive indices.

FIGS. 5A-5B shows the precedence flow-chart of the process options ofthe present invention.

FIG. 6A depicts the geometric optics problem of vignetting suffered byPrior Art processes.

FIG. 6B shows the general ray trace solution of the new process of thepresent invention to prevent vignetting off the photodetector activearea.

FIG. 7 is a diagram used to explain an optical path of incident light tothe photodetector active area, according to the present invention.

FIG. 8A shows the color pixel arrangement along a first principal axisperpendicular to the plane of the cross-section of the semiconductorimaging device.

FIG. 8B shows the color pixel arrangement along a second principal axisorthogonal to the first principal axis of FIG. 8A and perpendicular tothe cross-sectional plane of the semiconductor imaging device.

FIG. 9 illustrates a possible pixel combination for color imagesynthesis corresponding to the arrangement of color filters shown inFIG. 8.

DETAILED DESCRIPTION

The present invention discloses a significantly simplified fabricationsequence and the specific optical conditions and materials' propertiesto be satisfied in forming a planar film layer of high transmittancematerial over at least one layer of color filters to enable highefficiency integrated semiconductor array color imaging devices withoutmicrolenses.

FIG. 5A and FIG. 5B depicts the simplified comparative fabricationflow-charts of the new process of the present invention whichdistinguish it from the sequence of the Prior Art process. In accordwith the flow-charts shown, the manufacturing method of the presentinvention teaches priority formation of a high transmittance planarizinglayer directly above a color filter layer residing above the sensorelements of the matrix array comprising the semiconductor imager. In thePrior Art process exhibited in FIG. 5A option 1 deposits planarizationlayer 47 prior to color filter formation 48. In FIG. 5A option 2eliminates the planarizing layer and directly deposits the primary colorfilters 48 above the photodiode array. By contrast, FIG. 5B disclosestwo options, both of which teach a final special layer 49; in option 1,special layer 49 is deposited after planarizing layer 47 and colorfilter layer 48 are formed; in option 2, layer 49 follows directdeposition of the color filter layer above the photodiode portion of thepixel.

FIG. 6A exhibits the image light collection problem suffered in PriorArt processes and structures. In FIG. 6A, incident image light 9 fromthe camera optics is incident normal to the surface of the solid-stateimager, passing from a region of index of refraction N=1 (air) into thesemiconductor film layers with typical resin refractive index of N=1.6.Refraction of the ray bundle results in the outermost rays missing theimage plane (vignetting) comprised of the photosensor active area, and,impinging on the spaces between the photodiode elements. Light arrivingoutside the photoelectronic portion of the pixel diminishes sensitivity,signal-to-noise contrast, and induces the phenomenon referred to as“smear” related to the cross-talk effect.

The new process of the present invention is illustrated in FIG. 6B whichshows a simple ray-trace for the case of direct deposition of the colorfilters above the photosensor portion of the pixel followed by aspecified planarizing layer. In FIG. 6B, normal incident image light 9to the planarizing surface 50 enters from air to a material, such as aresin or polymer, of refractive index N closely matched to that of thecolor filter layer, and, suffers significantly less refraction at theindex interface surface 51, to arrive at the image plane to fill theactive area of the photodiode 14 to a very high order of approximation.A typical case is illustrated for air N=1.0, planarizing layer N=1.5,and for the color filter layer N=1.6.

An important attribute of the new colors only process of the presentinvention is the conformal concave contour of the interface surface 51shown in FIG. 6B between the color filter layer produced by directdeposition above the photodiode array 14 of the CCD imager. Thisrefractive index surface contour corresponds to the topology of the CCDsemiconductor device shown in FIG. 8A and FIG. 8B in the region abovethe pn-junction 57. FIG. 7 explains the optical physics of the affect ofincreasing the difference in the index of refraction across the “pixelsurface” 51:

light ray 9 incident to the “pixel surface” 51 at an angle θ₁ to thesurface-normal from a medium of index N₁ is refracted at an angle.theta.2 depending on the value of the refractive index N₂, according toSnell's Law of Refraction:N₁ Sin θ₁=N2 Sin θ₂  eq.(1)

If N1>N2, then θ₂>θ₁.

For example, if N₁=1.10 (air) and N₂=1.6 (color filter layer), and ifθ₁=30 degrees, then θ₂=18 degrees. But, if N₁=1.5 (specified planarizinglayer) and N₂=1.6 (color filter layer) and θ₁=30 degrees, then θ₂′=28degrees (where ′ denotes “prime”).

FIG. 8A depicts the cross-sectional view of the preferred embodiment ofthe present invention, showing in particular the priority formation ofthe color filter array in mutual registration with the photoactiveregions of the solid-state array imager. FIG. 8A illustrates the case ofa CCD imager fabrication sequence, but it is clearly recognized that thepresent invention equally well applies to charge-injection device (CID)imagers and CMOS imagers. In FIG. 8A, an “n” (negative) typesemiconductor substrate 52, is photolithographically patterned bysuitable photoresist coating, masking, exposing and developing, to openregions for ion-implant or diffusion doping by selected impurity atomsto form p-(weakly doped positive) type wells 53 and 54. With similarphotolithography steps, ion-implants or diffusions, an n+ type region 55is formed to create a pn-junction photodiode and a vertical chargecoupled device 56. A highly doped positive impurity, p++, is introducedselectively to form a surface isolation layer 57, and, a p-type well 58is formed to isolate the CCD device 56. To isolate pixels, a p+ channelstop 58 is formed. The gate insulator 59 is then applied over thesurface of the substrate. The vertical profile is completed byprocessing successive additions of transmission gate 60, interlevelinsulator 61, light-shielding layer 62, passivation layer 63, optionalplanarization layer 64 (cf., FIG. 5B option 1), and in accord with thepreferred embodiment of the present invention, color filters 65 for blue(also denoted B) and 66 for green (also denoted G).

FIG. 8B exhibits the second dimension of the color filter planeformation process, showing the orthogonal direction to that of FIG. 8A.All other semiconductor device structures remain the same for bothfigures. FIG. 8B shows the pixel sequence with the color filter 68 forred (also denoted by R) and the adjacent color filter 65 for blue (B).The color only process is then completed with the deposition of anencapsulant and planarization layer 67, as specified in accord with thepresent invention. Thus, the two-dimensional array of color filtersprovides the color pixel arrangement for synthetic reconstruction ofcamera images without microlenses. FIG. 9 illustrates a possible RBGcolor pixel arrangement, shown inscribed within the dashed-line.

The processes and structures shown in FIG. 8 will inherently create thepixel surface 51 of FIG. 6 by the conformal nature of the process filmdeposition in forming the color filter layer(s) above the photodioderegions of the imaging array. The present invention corrects thisinherent concave pixel surface with the index matching planarizing layerdirectly deposited after color filter layer formation. Without anindex-matched interface, the concave-up pixel surface will behave as aconcave (negative or diverging) lens element and result in overfillingthe photodiode active area. The features described here are highlyreproducible since they result from precision lithographic patterningand overlays. The resulting structure provides a high degree of finaltop surface flatness which eliminates the topography problems forentrapment of residual particles after package dicing and cleaning.

The resulting colors only imaging device has, therefore, eliminated thecomplex and costly steps of Microlens formation while sustaining highlight collection and pixel sensitivity with reduced cross-talk.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

1. A method for forming a color imaging device, comprising: providing asubstrate with a photosensor disposed thereon; depositing a passivationcoating above the photosensors; depositing a color filter layer over thepassivation coating; and forming an upper layer over the color filterlayer, the upper layer having an index of refraction that closelymatches an index of refraction of the color filter layer.
 2. The methodfor forming a color imaging device according to claim 1, wherein theforming step includes forming the upper layer directly on the colorfilter layer without forming a microlens layer.
 3. The method forforming a color imaging device according to claim 1, wherein the upperlayer has a planar top surface.
 4. The method for forming a colorimaging device according to claim 1, further comprising forming a firstoptically transparent planarizing encapsulant layer on said passivationcoating, before depositing the color filter layer.
 5. The method forforming a color imaging device according to claim 1, wherein the upperlayer is a planarizing layer comprising an antireftlection coating. 6.The method for forming a color imaging device according to claim 1,wherein the upper layer comprises a photoresist.
 7. The method forforming a color imaging device according to claim 1, wherein the upperlayer has an index of refraction in the range 1.5 to 1.65.
 8. The methodfor forming a color imaging device according to claim 1, wherein theupper layer has an index of refraction of 1.5, and the color filterlayer has an index of refraction of 1.6.
 9. The method for forming acolor imaging device according to claim 1, wherein the color imagingdevice is one of the group consisting of CMOS, CCD, and CIDsemiconductor devices.
 10. The method for forming a color imaging deviceaccording to claim 1, wherein said upper layer is comprised of aphotoresist.
 11. The method for forming a color imaging device accordingto claim 1, further comprising forming a photoshield layer over saidphotosensor, before depositing the passivation coating.
 12. The methodfor forming a color imaging device according to claim 1, wherein thecolor filter layer comprises red, green and blue color filters,respectively.
 13. A method for forming a color imaging device,comprising: providing a substrate with a photosensor disposed thereon;forming a light shield layer above said photosensors; depositing apassivation coating above the light shielding layer; forming a firstoptically transparent planarizing encapsulant layer on said passivationcoating depositing a color filter layer on the first opticallytransparent planarizing encapsulant layer; and forming an upper layerover the color filter layer, the upper layer having an index ofrefraction that closely matches an index of refraction of the colorfilter layer.
 14. The method for forming a color imaging deviceaccording to claim 13, wherein the forming step includes forming theupper layer directly on the color filter layer without forming amicrolens layer.
 15. The method for forming a color imaging deviceaccording to claim 14, wherein the upper layer has a planar top surface.16. The method for forming a color imaging device according to claim 13,wherein the upper layer is a planarizing layer comprising anantirefiection coating.
 17. The method for forming a color imagingdevice according to claim 13, wherein the upper layer comprises aphotoresist.
 18. The method for forming a color imagine device accordingto claim 13, wherein the upper layer has an index of refraction in therange 1.5 to 1.65.
 19. The method for forming a color imaging deviceaccording to claim 13, wherein the color imaging device is one of thegroup consisting of CMOS, CCD, and CID semiconductor devices.
 20. Themethod for forming a color imagine device according to claim 13,wherein: the forming step includes forming the upper layer directly onthe color filter layer without forming a microlens layer; the upperlayer has a planar top surface; the upper layer is a planarizing layercomprising an antireflection coating; the upper layer comprises aphotoresist; the upper layer has an index of refraction in the range 1.5to 1.65; and the color imaging device is one of the group consisting ofCMOS, CCD, and CIDsemiconductor devices.